1. Field of the Invention
The present invention is directed to an orifice fitting for measurement of fluid flow in a system wherein a plate carrier may be raised out of the fluid flow path in the system for service and maintenance without interrupting or disabling fluid flow.
2. Prior Art
While fluid may be measured with various types of meters such as positive displacement meters, turbine meters, and venturi meters, orifice meters are widely used in the field and in pipeline systems.
Fluid flowing through a pipe can be measured by placing a constriction, such as an orifice plate, in the line to cause a pressure drop as it flows through the orifice plate. There is a direct relationship between the amount of this pressure drop, called the differential pressure, and the rate of flow.
Extensive use is made of orifice fittings of various types. The inlet side of the fitting is connected to the upstream section of pipe, while the outlet side is connected to the downstream section.
Two types of orifice fittings are commonly employed. The junior or "simplex" fitting has a single orifice chamber wherein the orifice plate is mounted in place in the flow path of the pipeline. In order to remove the orifice plate for maintenance or servicing, the fluid pressure in the pipeline must be removed so that the fitting can be disassembled. In the second type of orifice fitting, a senior or "duplex" fitting, two separate chambers are provided, one lower chamber to hold the orifice plate in position for passage of fluid through the pipeline and a second upper chamber wherein access is provided for service and maintenance. A valve is typically provided to separate the compartments from each other. As an example, see Critendon U.S. Pat. No. 4,014,366, for a device to convert a junior fitting to a senior fitting.
There is a need, therefore, to provide an orifice fitting wherein access may be had to both the orifice plate and the various carrier plate seals without interrupting fluid flow through the lower chamber and without disabling the fitting.
It is also desirable to provide an orifice fitting which provides access to both sides of the carrier plate.
The horizontal and vertical alignment of the orifice opening in the orifice plate with the tube or pipeline is critical both for accuracy of flow measurement and because of regulations, such as American Petroleum Institute regulations. An example of a mechanism to concentrically align the orifice is shown in Crane, U.S. Pat. No. 5,327,938 and Klak, U.S. Pat. No. 5,305,796.
It is, therefore, also desirable to provide an orifice fitting to provide concentric alignment of the orifice and orifice plate when in the lower chamber.
It is also desirable to provide an orifice fitting that may be raised out of the fluid flow path or lowered into the fluid flow path through a motorized mechanism.
Fluid in the system is often under considerable pressure and care must be taken to observe precautions.
It is also desirable to provide an orifice plate fitting wherein inspection and maintenance may be performed on the orifice plate after determining and confirming that the upper chamber is not pressurized.
It is also desirable to provide an orifice fitting with the ability to verify that no fluids bypass around the O-rings of the carrier.
The teachings of the present invention may also be employed in a gate valve. A plate may be lowered into or out of the fluid flow path. It is desirable to provide a gate valve having a full bore that will allow flow therethrough without any restriction in flow. It is also desirable to provide a gate valve wherein access is provided to the plate without disabling the valve.